The present invention relates to size compositions, sized glass fibers and their use.
The properties of composites of glass fibers and polymers are affected to a large extent by the shear strength between the glass fibers and the polymer matrix surrounding the glass fibers. The task of the size is to produce this composite structure between the glass fiber and the matrix polymer and at the same time to ensure the producibility and processability of the glass fibers. Compositions consisting of water, a polymeric binder (the so-called film-former), an adhesion promoter, lubricants, anti-static agents and other auxiliary substances are used as sizes. Organic, water-dispersible or water-soluble polyvinyl acetate, polyester-epoxide, polyurethane, polyacrylate or polyolefin resins or mixtures thereof are generally used as binders.
Film-formers and adhesion promoters are generally selected so that there is an affinity between the polymer matrix and the film-former and/or adhesion promoter and thus a mechanical composite is formed between the glass fibers and the polymer matrix. It is therefore understood that the formulations for sizes have to be optimised to the particular polymer matrix and that the properties of the composites respond in a sensitive manner to changes in the size composition.
In the case of partly crystalline thermoplasts, the crystallinity (ratio of crystalline to amorphous regions; crystal morphology) of the polymer in regions surrounding the glass fibers may also be affected by the size.
It is known that certain organic or inorganic substances can act as nucleating agents for partly crystalline thermoplasts, i.e. they act as a seed-producer for crystal growth in the partly crystalline polymers. The nucleating effect depends on the interaction (e.g. steric interactions, hydrogen bridge bonds) of the surface of the nucleating agent with the polymer chains. The polymer chains become ordered due to interactions on the surface, which means that crystal growth is initiated or encouraged. Seed-producers or nucleating agents are used in particular during the preparation of compounds where the acceleration of crystallisation and/or homogeneous seed-production is desired. Homogeneous seed-production normally leads to smaller crystallites with more uniform size distribution and can thus lead to an improvement in mechanical properties such as toughness and strength. The seed-producing effect of nucleating agents takes place, in composites which contain glass fibers, from the matrix. Under the production conditions for nucleated, glass fiber reinforced compounds, the nucleating agent is added as a solid or in the form of a concentrate during the compounding process and distributed uniformly in the matrix.
The object of the present invention is to provide polymer composites (composites of polymer and glass fibers) which have especially good mechanical properties such as, for example, toughness and strength.
This object can be achieved, surprisingly, by specific size compositions and with glass fibers which are sized with these specific size compositions. Size compositions according to the invention contain, in addition to water-dispersible or water-soluble polyepoxides, polyesters, polyvinyl acetates, polyacrylates and/or polyurethanes as film-former, organofunctional silanes as adhesion promoters and other conventional size constituents, organic or inorganic nucleating agents with particle sizes  less than 300 nm which are practically insoluble in polymer melts, for example in polyamides, in polypropylenes and in polybutylene terephthalates.